A leading cancer charity has described as "extremely worrying" new research which found women who put off having children until they reach their 30s are at increased risk of breast cancer.

But Delyth Morgan, chief executive of the charity, Breakthrough Breast Cancer, says women should not assume the age they have children is the only factor determining whether or not they get cancer.

The study, published in the British Journal of Cancer, also found the rising number of girls who start their periods early have a higher chance of developing the debilitating disease which strikes 38,000 women a year in the UK.

But having a miscarriage does not increase the risk of breast cancer at any age, the study of more than 90,000 women found.

Professor Gordon McVie, joint director general of Cancer Research UK, said abortion would also have no effect as it is biologically similar to miscarriage.

Compared with those who gave birth before the age of 22, women who had their first child in their 30s were 63pc more likely to develop breast cancer before the menopause and 35pc more likely to get the disease afterwards.

Professor Robin Weiss, editor of the British Journal Of Cancer, added: "There is a one in nine chance of getting breast cancer for all women and those who don't have children, or have them late, have a higher chance, whereas those who have lots young, have a lower chance."